Apparatus for registering a mask pattern in a photo-etching apparatus for semiconductor devices

ABSTRACT

An apparatus is provided for registering a pattern on a mask plate with a pattern already formed on a semiconductor wafer. A reflector group is provided on the wafer comprising a plurality of reflectors having a predetermined shape, interval and alignment. Two window groups are provided at predetermined positions on the mask plate. Each window group comprises a plurality of windows having a predetermined shape, interval and alignment that corresponds to the shape, interval and alignment of the reflector group. One of the window groups is provided with a staggered phase relationship with the other window group such that when one of the wafer or the mask plate is moved relative to the other, variations in the quantity of light reflected by the reflector group and passed through the respective window groups is used to determine the relative position of the wafer and the mask plate.

This is a division of application Ser. No. 213,960, filed Dec. 8, 1980,now U.S. Pat. No. 4,377,028.

The present invention relates to an apparatus for registering a patternon a mask plate with a pattern already formed on a semiconductor waferin the manufacture of semiconductor devices.

Recently, the size of patterns used to manufacture semiconductor deviceshas become more and more minute, and accordingly, in place of theso-called one-shot exposure process in which exposure is effected in oneshot over the entire wafer surface, a process of repeatedly effectingexposure through one or a few patterns which are included within an areaof, for example, about 10 mm square is being employed. In suchphoto-etching processes, either an X-Y stage having extremely highprecision is used to repeatedly position the wafer and make exposures orafter a wafer has been moved by one pattern length by means of an X-Ystage, a mask pattern is registered with a pattern already formed on awafer by any appropriate means and then exposure is effected. However,the former process requires that the X-Y stage should be extremelyprecise, and the latter process is accompanied by various difficultiesin quickly positioning a wafer relative to a mask plate at highprecision because the pattern formed on the wafer is generally extremelysmall and hence light reflected by this pattern is also very faint. Inthe process of repeatedly effecting exposure many times on a singlewafer through a pattern plate, it is especially difficult to quicklymove an X-Y stage and quickly effect registration of the patterns.

It is therefore one object of the present invention to provide anapparatus for quickly and precisely registering, a pattern on a maskplate with a pattern already formed on a semiconductor wafer in aphotoetching apparatus for semiconductor devices.

Another object of the present invention is to provide a novel apparatusfor registering a pattern on a mask plate with a pattern already formedon a semiconductor wafer in a photo-etching apparatus for semiconductordevices, in which a reference target such as a reflector group to beused for registering the patterns is provided on the wafer in suchmanner that said reference target does not obstruct the manufacture ofthe semiconductor devices.

In order to achieve the aforementioned objects, according to one featureof the present invention, there is provided an apparatus for registeringa pattern on a mask plate with a pattern already formed on asemiconductor wafer, comprising a wafer support for holding thesemiconductor wafer, a mask support for holding the mask plate, anoptical system including a lens for focusing an image of the pattern ofthe mask plate on the semiconductor wafer and a light source forirradiating the wafer. The wafer is provided with a plurality ofreflectors of predetermined shape aligned at predetermined intervalsalong a predetermined direction. The mask plate is provided with twowindow groups at predetermined positions on the mask plate incorrespondence to the position of the reflector group on the wafer. eachwindow group consisting of a plurality of windows of predetermined shapealigned at the same intervals along the same direction as the reflectorgroup, one window group being staggered in phase with respect to theother window group. Apparatus is provided for moving one of the waferand the mask plate relative to the other in the direction of alignmentof the reflectors and windows while irradiating the reflector group withlight, detecting the quantities of light reflected by the reflectorgroup and passed through the respective window groups by means ofrespective photo-sensitive means, and determining the relative positionof the wafer and the mask plate where the detected respective quantitiesof light take a predetermined proportion to thereby determine therelative position where the pattern on said mask plate is registeredwith the pattern already formed on said semiconductor wafer. Embodimentsof the invention are also contemplated wherein two reflector groups in astaggered phase relationship are provided with a single window group.

The above-mentioned and other features and objects of the presentinvention will become more apparent by reference to the followingdescription of preferred embodiments of the invention taken inconjunction with the accompanying drawings, wherein:

FIG. 1 is a general schematic view of a photoetching apparatus forsemiconductor wafers according to the present invention,

FIG. 2 is a schematic plan view showing an outline of arrangement of areflector group and two window groups to be used in the photo-etchingapparatus according to the present invention,

FIG. 3 is an enlarged schematic plan view showing one example of a partof the reflector group,

FIG. 4 is an enlarged schematic plan view showing another example of apart of the reflector group,

FIG. 5 is a diagram showing variations of quantities of light detectedby two respective photo-sensitive means,

FIG. 6 is a diagram showing a variation of a difference between thequantities of light detected by the two respective photo-sensitivemeans, and

FIG. 7 is a schematic plan view showing locations of reflector groupsformed on a semiconductor wafer according to the present invention.

Referring now to FIG. 1 of the drawings, 1 designates an optical systemincluding a lens, which is used for projecting an image of a maskpattern for exposure on a mask plate 2 onto a semiconductor wafer 3 inan extremely reduced size, 4, 5 and 6 designate light paths uponexposure of the wafer 3 to the light through the mask plate 2, 9designates a laser device illustrated as one example of a light sourcefor irradiating a reflector group 27 in FIG. 2 formed on the wafer 3, 8designates a path of light emitted from the laser device 9, and 7designates a path of light regularly reflected by the reflector group27. On the other hand, a number of arrows designated by numeral 10denote paths of light reflected by diffused reflection, and an arrow 11denotes a path of light reflected by the reflector group 27 and focusedby the optical system 1 onto the mask plate 2. In other words, thereflector group 27 on the wafer 3 is irradiated by the light emitterfrom the laser device 9, and the image of the reflector group 27 isprojected at the position of a window group 26 in FIG. 2 formed on themask plate 2. Photo-sensitive devices 12A and 12B which are illustratedin FIG. 1 as overlapped in the direction perpendicular to the sheet ofthe figure, are devices for measuring intensities of light projectedthereto, and each of them contains a photo-electric transducer therein.In addition, in FIG. 1 14 designates a wafer holder, and 15 designates amask plate holder.

On example of a reflector group 27 formed on the wafer 3 and windowgroups 26 formed on the mask plate 2 to be used for registering thewafer and the mask plate, is illustrated in FIG. 2. In the followingdescription, the invention will be explained assuming that referencenumeral 26 designates two window groups on the mask plate 2 andreference numeral 27 designates a reflector group on the wafer 3.However, it is to be noted that the present invention can also bepracticed by forming two reflector groups having the configuration shownat 26 on the wafer 3 and one reflector group having the configurationshown at 27 on the mask plate 2.

In the illustrated embodiment, the reflectors 24 look light when theyare viewed through the optical system 1, whereas the remaining area 22looks dark. The areas 25 and 23, respectively, represent two windowgroups A and B formed on the mask plate 2 and adapted to pass lighttherethrough. The light emitted from the reflectors 24 in the reflectorgroup 27 on the wafer 3 by diffused reflection, is passed through thewindows 23 or 25 and reaches the photo-sensitive device 12A or 12B. Thedevice 12A is adapted to receive the light passed through the windowgroup A in FIG. 2, whereas the device 12B is adapted to receive thelight passed through the window group B in FIG. 2.

Now an operational discussion is presented for registering a pattern onthe mask plate 2 with a pattern already formed on the semiconductorwafer 3.

With reference to FIG. 2, when the reflector group 27 and the windowgroups 26 are in the illustrated relationship in position along thedirection indicated by arrows 28, in the range designated by referencecharacter A, since the reflectors 24 in the reflector group 27 coincidein position with the windows 25 in the window group A, thephoto-sensitive device 12A will receive a maximum quantity of light.Whereas in the range designated by reference character B in FIG. 2,since the reflectors 24 in the reflector group 27 and the windows 23 inthe window group B are completely staggered in phase from each other,the photo-sensitive device 12B can receive only a minimum quantity oflight. In the illustrated example, if the intervals between adjacentreflectors or adjacent windows as indicated by arrows 20 are called onepitch, then on the mask plate 2 the window group A and the window groupB are said to be staggered in phase by 1/2 pitch from each other.Assuming now that the wafer (22 in FIG. 2) is moved in the direction ofarrow 29 relative to the mask plate (21 in FIG. 2), then in the rangedesignated by character A, since the overlap between the reflectors 24and the windows 25 decreases gradually, the quantity of light receivedby the photo-sensitive device 12A is reduced successively, whereas inthe range designated by character B, the overlap between the reflectors24 and the windows 23 increases gradually, and hence the quantity oflight received by the photo-sensitive device 12B is increasedsuccessively. It will be readily understood from the above descriptionthat when the wafer 22 has moved by 1/2 pitch relative to the mask plate21 in the direction shown by arrow 29, the quantities of light receivedby the photo-sensitive devices 12A and 12B are completely reversed. Ifthe former has moved by one pitch, then the relation between thequantities of light received by the photo-sensitive devices 12A and 12Breturns to its original relationship.

FIG. 5 shows relations between the quantities of light received by thephoto-sensitive device 12A and 12B, respectively, and the position ofthe wafer 22 moving in the direction of arrow 29 relative to the maskplate 21, the abscissa indicates the displacement of the wafer 22, andthe ordinate indicates the quantities of light received by therespective photo-sensitive devices 12A and 12B. (Generally in aphoto-sensitive device including a photo-electric transducer element, avariation of a quantity of light is converted into a variation of anelectric current or a voltage.)

In this figure, a solid line curve 51 indicates the quantity of lightreceived by the photo-sensitive device 12A, while a dash line curve 52indicates the quantity of light received by the photo-sensitive device12B. Points 55 and 56 on the respective curves 51 and 52 represent themoment when the wafer 22 and the mask plate 21 are in the positionalrelationship illustrated in FIG. 2, and subsequently as the wafer 22 ismoved in the direction of arrow 29 shown in FIG. 2, the quantities oflight received by the respective photo-sensitive devices 12A and 12Bwould vary along the respective curves 51 and 52 in the direction ofarrow 57 in FIG. 5. Points 58 and 59 on the respective curves 52 and 51represent the moment when the wafer 22 has been moved by 1/2 pitch fromthe relative position shown in FIG. 2.

A curve 61 shown in FIG. 6 represents a difference obtained bysubtracting the quantity of light received by the photo-sensitive device12B from the quantity of light received by the photo-sensitive device12A. Since the quantities of light received by the respectivephoto-sensitive devices 12A and 12B are converted into currents orvoltages, such arithmetic operations can be easily performed. Asillustrated in FIG. 6, the curve 61 representing the difference swingsboth in the positive and negative directions relative to a zero levelline, that is, an abscissa 62. Referring now to point 63 where the curve61 crosses the abscissa 62 (that is, the point corresponding to a point54 in FIG. 5 where the curves 51 and 52 cross with each other), thispoint means that the quantity of light received by the photo-sensitivedevice 12A is equal to the quantity of light received by thephoto-sensitive device 12B. In other words, at the point 63 the relativeposition between the wafer 3 and the mask plate 2 is displaced by 1/2pitch from the relative position illustrated in FIG. 2. Although thequantities of light passed through the window groups A and B,respectively, may be varied by many causes other than the relativedisplacement between the wafer 3 and the mask plate 2, in such casesthey would vary in substantially the same manner both in the region Aand in the region B. Therefore, if the positions of the reflector group27 and the window groups A and B on the wafer 3 and the mask plate 2,respectively, are preselected at such positions that when a curve 61 asshown in FIG. 6 is depicted by calculating the difference between thequantities of light passed through the window groups A and B,respectively, and detected by the photo-sensitive devices 12A and 12B,respectively, the points where the curve 61 crosses with the 0-levelline such as points 63, 64, etc. may correspond to the position where animage of a pattern formed on the wafer 3 coicides with a mask pattern onthe plane of the mask plate 2, then very conveniently the relativeposition between the wafer 3 and the mask plate 2 can be achievedaccording to the variations of the quantities of light received by therespective photo-sensitive devices 12A and 12B, respectively.

Now a method for forming the reflector group 27 on the wafer 3 will bedescribed in connection with two examples.

The reflector group 27 is formed in the first etching step for etching apattern on a silicon oxide film formed on a silicon wafer 3 through aphoto-resist mask, and so, it consists of silicon oxide film portionsand etched silicon wafer portions. Two different examples of thereflectors 24 formed on the wafer 3 as shown in FIG. 2 are illustratedin FIGS. 3 and 4, respectively. Each reflector represented by a singleframe 24 in FIG. 2 is formed of a large number of small reflectorregions such as a large number of thin slit regions 30, 31 or 32 in FIG.3 or a large number of small square regions 40, 41 or 42 in FIG. 4.

When the light emitted from the light source 9 is projected along thelight path 8 onto such thin slit regions 30, 31 or 32 or such smallsquare regions 40, 41 or 42, while the light reflected regularly by thesilicon oxide surface propagates mostly along the direction shown byarrow 7, at the reflector regions 30, 31, 32, 40, 41 or 42, diffusedreflection occurs at the edge portions of these reflector regions asshown by arrows 10 in FIG. 1, and the light of the diffused reflectionis focused by the optical system 1 on the plane of the mask plate 2. Inthis way, by forming each reflector 24 of an assembly of small reflectorregions such as thin slots, the light reflected by the edge portions ofthe small reflector regions can be collected as diffused reflectionlight by the optical system, and thus the quantity of light received bythe photo-sensitive device can be increased. It is to be noted that theregion surrounding these small reflector regions reflects only a minutequantity of light and looks dark. However, even if this dark region andthe small reflector regions which reflect a large quantity of light areformed in a reversed fashion, the effect of the present invention can beachieved equally.

FIG. 7 illustrates the reflector groups disposed in an exemplary fashionon a semiconductor wafer. Since the reflector groups can be formed inelongated shapes, the reflector groups can be arranged on a cutting linebetween adjacent semiconductor chips as shown in FIG. 7. In this figure,reference numerals 71 and 72 designate patterns for forming IC chips,numerals 74 and 76 designate reflector groups to be used for registeringthe patterns 71 and 72, respectively, with a pattern on a mask platealong an X-direction, and numerals 73 and 75 designate reflector groupsto be used for registering the patterns 71 and 72, respectively, with apattern on a mask plate along a Y-direction.

Owing to the above-described features, the present invention makes itpossible to quickly and easily register a pattern on a semiconductorwafer with a pattern on a mask plate.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not as a limitation to thescope of the invention.

What is claimed is:
 1. An apparatus for registering a pattern on a maskplate with a pattern already formed on a semiconductor wafer;characterized in that said apparatus comprises means for holding saidsemiconductor wafer, means for holding said mask plate, an opticalsystem including a lens for focusing an image of the pattern of saidmask plate on said semiconductor wafer, a light source for irradiating awafer held by said wafer holding means, said mask plate having aplurality of windows having a predetermined shape, aligned at apredetermined pitch along a predetermined direction, said wafer having aplurality of reflectors of a predetermined shape aligned at apredetermined pitch along a predetermined direction, one of said windowsand said reflectors being directed into first and second groups, saidfirst and second groups being provided with a staggered phaserelationship equal to a multiple of one half of said predeterminedpitch, means for moving one of said wafer and said mask plate relativeto the other, and first and second photo-sensitive means adapted toreceive light emitted from said light source, reflected by reflectorsformed on said semiconductor wafer and passed through said windowsformed on said mask plate, said first photo-sensitive means beingresponsive to light received from said first group and said secondphoto-sensitive means being responsive to light received from saidsecond group, whereby the relative position of said wafer and said maskplate are determined when the detected quantities of light received bysaid first and second photo-sensitive means take a predeterminedproportion to thereby register the pattern on said mask plate with thepattern already formed on said semiconductor wafer.
 2. The apparatus ofclaim 1 wherein each of said reflectors comprises a large number ofsmall reflector regions of predetermined shape.
 3. The apparatus ofclaim 1 wherein each of said reflectors comprises a large number ofsmall reflector regions of predetermined shape which can reflect only asmall quantity of light, said small reflector regions being surroundedby regions adapted to reflect a large quantity of light.
 4. Theapparatus of claim 1 wherein the relative position of said wafer andsaid mask is determined when the quantity of light received by saidfirst photo-sensitive means and the quantity of light received by saidsecond photo-sensitive means are equal.
 5. The apparatus of claim 1wherein said reflectors are formed on a cutting line between adjacentintegrated circuit chips on said semiconductor wafer.